1. Field of the Invention:
The present invention relates to a process for producing granule coated with a tannic acid metal chelate compound (hereinafter referring to as a tannic acid metal chelate-coated granule). More particularly, it relates to a process for producing a tannic acid metal chelate-coated granule which is less pulverizable and has a particle size of 100 mesh on (remained on 100 mesh sieve in Japanese Industrial Standard) at high yield and which imparts excellent adsorbability as a filter for smoke of a cigarette.
2. Description of the Prior Art:
The smoke formed by smoking a cigarette is usually classified into particle phase components and gas phase components. The particle phase components essentially consist of alkaloid such as nicotine and tar and water. On the other hand, the gas phase components essentially consist of acetaldehyde, isoprene, acetone and steam. Certain chemical components being undesirable for smoking hygiene and smoke taste are included among the components. In order to absorb the undesirable chemical components by a filtration and to impart light smoke taste, it has been proposed to connect a filter to a cigarette or to incorporate one of various additives in a filter or to fill the additive with a filter.
Cellulose acetate, paper, pulp or non-woven fabric has been mainly used as a material for the filter to remove the particle phase components. As the additives, it has been proposed to use activated carbon, tannic acid or extract of coffee or tea which contains tannic acid U.S. Ser. No. 134713 and U.S. Pat. No. 3,319,630), tannic acid metal chelate compound (Japanese Unexamined Patent Publication No. 76300/1976) and activated carbon and tannic acid metal chelate compound (Japanese Unexamined Patent Publication No. 99399/1978). The tannic acid metal chelate compound improves a separation factor for tar and nicotine and adsorbs acetaldehyde, isoprene and acetone and improves smoke taste.
The tannic acid metal chelate compound is usually produced by mixing an aqueous solution of tannic acid with an aqueous solution of a metal salt and adding a base such as sodium hydroxide and ammonia to adjust to pH of 7.0 to form a water insoluble tannic acid metal chelate compound and washing it with water and pulverizing it to use in a form of powder or ganule.
In the powdery form, it is dusty to be inconvenient for handling and the fine powder is sucked with the smoke and moreover, it is difficult to uniformly distribute in a filter and it is not enough to impart the desired absorbability. Therefore, it is preferable to use it in the uniform granular form in comparison with the powdery form. The conventional granule has been produced by forming a slurry of powdery tannic acid metal chelate compound and extruding the slurry through a sieve into a pellet form and pulverizng it after drying it and then sieving it through a desired sieve. The sieved product (hereinafter referring to as the pulverized product) having a desired particle size can be obtained. However, the yield of the pulverized product having a desired particle size is low and a distribution of the particle size is not uniform and is easily pulverized. Moreover, a loss of the tannic acid metal chelate compound is large and the reuse of the sieve pass is not easy to be economical disadvantage.